Data from the Office for National Statistics published Thursday shows how important foreign-owned firms are for Britain’s economy. In 2011, foreign-owned companies represented just 1% of all firms but a whopping 28% of U.K. gross value added, a measure of the income businesses generated less their costs in producing that income. That equated to about £270 billion ($436 billion) of income that year, the ONS said.

Looking just at big firms employing more than 250 people, foreign-owned enterprises represented 28% of the total number of U.K. companies in 2011 and a massive 40% of those firms’ combined income.

And which country accounted for the highest share of foreign ownership? Far and away, it was the U.S.. Americans owned 5,423 businesses in the U.K., and in 2011 that contributed £86.4 billion of that £270 billion total income.

More than 3,000 firms were French- or German-owned. The Chinese didn’t make the list, perhaps surprisingly, considering how often lawmakers fret about Beijing’s involvement in the U.K. economy.

What might set alarm bells ringing is that in 2011 another 3,000 or so companies’ owners were based in territories including Jersey, Luxembourg, Bermuda, the Cayman Islands, Guernsey, the British Virgin Islands and the Isle of Man, all jurisdictions (in)famous for their extremely competitive tax regimes.

Prime Minister David Cameron and Chancellor of the Exchequer George Osborne have made cracking down on tax avoidance a major goal of policy. The ONS said Thursday’s data is a snapshot of 2011 and they don’t yet have more recent information on whether that number has gone up or down since.